When the TARDIS was attacked by the Rani, the Sixth Doctor was injured and forced to regenerate. After a brief period of post-regenerative confusion and amnesia, the Seventh Doctor thwarted the Rani's plans, and rejoined his companion Mel.
After Mel left, the Doctor was joined by time-stranded teenager Ace.Although he did not mention it at the time, the Doctor soon recognised that the ancient entity known as Fenric was responsible for the Time Storm which transported Ace from 1980's Earth to Svartos in the distant future. The Doctor took Ace under his wing and began teaching her about the universe, all the while keeping an eye out for Fenric's plot.
The Doctor began taking a more active approach to defeating evil, using the Hand of Omega as part of an elaborate trap for the Daleks which resulted in the destruction of their home planet and another Time Lord relic to destroy a Cyberman fleet. The Seventh Doctor's manipulations were not reserved for his enemies. With the goal of helping Ace confront her past, he took her to a Victorian house which she had burned down in 1983. Eventually, the Doctor confronted and defeated Fenric at a British naval base during WWII, revealing Fenric's part in Ace's history.
The 7th incarnation of the Doctor met his end when landing in 1999 San Fransisco. Stepping out of the TARDIS into the middle of a gang shoot-out he was quickly gunned down...